Paints composed mainly of a melamine resin such as alkyd-melamine resin or acrylic melamine resin have been conventionally used for coating automobiles, industrial equipments, steel furnitures, interior and exterior of buildings, household electric appliances, plastic products and the like.
However, such paints composed mainly of a melamine resin has problems that harmful formaline is generated at the time of curing, and that the cured coating films are attacked by acid rain because they are poor in acid resistance. In particular, the problem of acid rain resulting from air pollution assumes a serious aspect in recent years, and there is observed a phenomenon that etching, whitening or spotting occurs in the coating films.
In order to solve the problems, it is proposed to use, in paints, a blend of a vinyl copolymer having a hydrolyzable silyl group and an acrylic polyol, or a copolymer of a vinyl monomer having a hydrolyzable silyl group and a vinyl monomer having an alcoholic hydroxyl group.
The use of a blend of a vinyl copolymer having a hydrolyzable silyl group and an acrylic polyol, or the use of a copolymer of a vinyl monomer having a hydrolyzable silyl group and a vinyl monomer having an alcoholic hydroxyl group has the advantage that coating films formed therefrom are superior in acid resistance and weatherability as compared with paints composed mainly of a melamine resin such as acrylic melamine or alkyd-melamine resin, since the hydrolyzable silyl group and the alcoholic hydroxyl group form stable siloxane bonds or siloxy bonds to cure.
However, in case of using a blend of a vinyl copolymer having a hydrolyzable silyl group and an acrylic polyol, or a copolymer of a vinyl monomer having a hydrolyzable silyl group and a vinyl monomer having an alcoholic hydroxyl group, the scratch resistance is not always sufficient. It is proposed to introduce a flexible component having a polyester structure in order to impart a scratch resistance. However, there is a case that the introduction rather lowers the acid resistance and hardness, so this proposal is not satisfactory in this respect.
For example, in case of top coat finishing of automobiles, metallic color finishing and solid color finishing have been generally adopted. In case of the solid color finishing, an alkyd-melamine resin paint has been conventionally used and generally cured in a one coat-one bake manner. Recently, in compliance with strict demands of properties such as appearance of finishing, weatherability, acid resistance and scratch resistance, it is proposed to coat on the solid color finishing a clear paint, e.g., an acrylic-melamine resin paint, a paint containing the above-mentioned blend system of a hydrolyzable silyl group-containing vinyl copolymer and an acrylic polyol, or a paint containing a vinyl copolymer having both a hydrolyzable silyl group and an alcoholic hydroxyl group in the same molecule. In this case, it is also proposed to introduce a flexible component having a polyester structure into the clear paint resin in order to raise the scratch resistance, but it is known that the acid resistance and hardness are not always satisfactory.
Thus, it is an object of the present invention to provide a curable topcoat composition which not only exhibits excellent acid resistance and scratch resistance, but also is excellent in balance of physical properties of coating films such as weatherability, appearance and hardness.
Another object of the present invention is to provide articles coated with the curable composition.